October 2019

Sud-Est SNCASE S.E.3000 Lateral-Twin Helicopter

First flight: October 23, 1948

Post-war French-built version of the Focke-Achgelis Fa 223 ‘Drache’ (Dragon), 
which had a first flight on June 12, 1940

The Société Nationale de Constructions Aéronautiques du Sud-Est (SNCASE, or just Sud-Est) was founded 1936 and became famous in the rotorcraft manufacturing with its Alouette II, while Sud-Ouest founded the same year worked on tip-jet driven helicopters Ariel I-III and finally the Djinn, before both merged to Sud Aviation in 1957. All helicopter activities began after WW II, at Sud-Est with the team of Henrich Focke from Germany; and at Sud-Ouest with Theodor Laufer, a partner of the Austrian von Doblhoff team. 

After WW II, in August 1945, Henrich Focke and nine of his team members were hired by the French SNCASE, who wanted them to rebuild the Fa-223 (first flight June 12, 1940) that now got the type name SE 3000. Initially they aimed for ten aircraft of that type, and an advanced version of the Fa-330 submarine rotary kite, but the latter was changed in favor for development of a small single main rotor helicopter SE.3101 that formed the basis for the very successful Alouette I and II rotorcraft. Their working location was in Argenteuil North West of Paris. Because the Moroccan troops had burnt a whole package of original drawings, the reconstruction of them, partly from pure remembering, was their first task. The detail design, construction and manufacturing was in cooperation with the Sud-Est staff, including some tensions due to very different working habits of both. Focke’s long lasting trials until clearance of a machine was naturally to the displeasure of the French, and eventually a French officer lost control: ”He is always afraid!” Focke answered: ”But from this sort of fear came the success.” From then on he was not attacked any more. However, responsibility moved more and more to the French that denied Focke to take the sole responsibility he requested. Eventually Focke’s negotiations with the British and successive cancellation of the French contract of him and his team in March 1947 caused imprisonment of all of them, which ended the cooperation on development of the SE 3000, and the remaining construction and manufacturing was in hands of Sud-Est.

The SE 3000 finally became airborne Oct. 23, 1948 (8 years after the Fa-223). It was a twin-rotor six-seater helicopter with a crew of two sitting side-by-side in the fully glazed cockpit and a four seat passenger cabin behind them. The 9-cylinder BMW Bramo Fafnir 323 R2 air-cooled radial engine was a little modified version of the 323 D used in the Fa-223, delivers up to 1000 hp for hovering, and 735 hp permanently, and was located behind the cabin. A steel-tube frame formed the fuselage, covered by fabric, with outriggers on either sides that carried the two three-bladed counter-rotating rotors of 12 m diameter with leaving 0.5 m space in the middle between the rotor disks. The T-tail consisted of a fin with rudder and an elevator strut-braced to it, both controllable by the pilot, and the landing gear was of the fixed three-wheel type with shock absorbers. In the center a power-driven crane was located for slung loads of up to 700 kg. The twisted rotor blades had a steel tube as main spar, wooden ribs, dual taper with the largest chord at 1/3 of the radius, were covered by plywood with a skin of impregnated fabric. Both rotors rpm were automatically compared to each other and in case of even small differences the blade collective pitch automatically switched to autorotation mode on both rotors. In latest Fa-223 versions the pilot could reverse this during flight, but that feature was not installed in the SE 3000.

Testing of the aircraft prevailed at Villacoublay until the end of 1950, at which time two more aircraft were built, until the French Government decided to cancel the program and to scrap the three vehicles. Jean Boulet, test pilot of the SE 3000, summarized his experiences that the aircraft had good longitudinal stability, but showed a dynamic instability in roll while hovering in ground effect and a static instability of roll in translation at low speed when a turn is engaged, and suggested an automatic controller to fix these deficits.

The side-by-side rotor concept never became a series production helicopter anywhere in the world, except for the tilt-rotor aircraft, but these are essentially fixed-wing aircraft with hovering capability and not helicopters. One major reason is the large space on ground required by this design, compared to single rotor helicopters, or tandem helicopters. However, because both rotors are virtually free from interferences with the fuselage, they have a superior hovering performance.

Photos: Airbus Helicopters

Text: Berend G. van der Wall

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